Rolling cone rock bit with wraparound spearpoints



May 26, 1964 F. H. MCELYA ETAL ROLLING CONE ROCK BIT WITH WRAPAROUND SPEARPOINTS Filed Jain. 31, 1962 FIGURE 2 United States Patent Ofi ice 3,134,447 Patented May 26, 1964 3,134,447 ROLLING CONE RQCK BIT W111i WRAPARGUND SPEARPOINTS Fred H. McEiya and Leon B. Stinson, Houston, Tex.,

assignors to Hughes Toni Company, Houston, Tex., a

corporation of Delaware Filed Jan. 31, 1962, Ser. No. 175,005 5 Claims. (Cl. 175332) The present invention lies in the field of rolling cutters for rock bits, and more specifically in the field of rolling cone cutters using wear resistant inserts or compacts rather than metal teeth. The latter type of rock bit is now well known in the art, the present invention residing in an improved cutting structure, particularly adjacent the apex of the cone, commonly referred to as the spearpoint. Since the cutters of the present invention use no spearpoint in the traditional sense of an elongated cutting structure extending toward the axis of the bit and terminating either on the opposite side or on the same side and closely adjacent thereto, it has received the cognomen wraparound spearpoint. In using compact bits of the three spearpoint type shown and described in the patent to Morlan, 2,774,571 and in other prior art compact bits, difficulty is frequently encountered in certain types of hard formations, e.g., taconite and bromide. In such formations, the base metal at the spearpoints of the cones is sometimes worn or broken away and the compacts fall out, allowing the formation of a large conical core at the center of the hole. When this condition obtains, there are no compacts left to resist further abrasion of the cone metal, with the result that the upstanding core increases in size as the hole deepens, at the expense of the cone metal, until the bearings are exposed. In an aggravated condition, the balls are loosened, the cones fall oif the bearing pins, and even very slow drilling comes to a halt.

It is an object of the present invention to provide a cutting structure on the noses or spearpoints of compact conical rolling cutters which resists and retards such abrasion. 7

Another object is to provide a rolling cutter using wear resistant cutting inserts in which the nose or spearpoint portion is modified to avoid loss of inserts and/or portions of cone shell metal in the nose.

A further object is to provide such a rolling cutter in which the cutting cone or shell furnishes greater support for the inserts in the nose thereof.

The general method of attaining such objects according to the present invention is by providing arolling cutter in which the nose portion is blunt in comparison with the similar portion of prior art rolling cutters, such cutter being adapted for mounting onabearing pin of a rock bit so that the blunt nose thereof terminates at a point spaced from the axis of rotation of such bit. At the same time, the number of compacts in each nose is reduced, thereby increasing the metal sections between adjacent compacts. A typical rock bit of the present invention has a multiplicity of such blunt-nosed cutters mounted thereon to terminate at points spaced from the bit axis so that the bit in operation drills a hole with an upstanding rock core or post of small but appreciable cross-section, and yet effectively drills a complete hole without premature destruction of the cutting structure in the nose portions of the cones. Such cutters are also useful on other rotary earth penetrating tools such as reamers, tunnel and shaft cutting machines, and core drills, i.e., a drill used to out a kerf in a rock formation and leave a large core which is severed and recovered with other equipment.

The present invention thus involves a marked departure from conventional rolling cutter rock bit structures,

wherein was embodied the philosophy that rock cores or posts must be avoided by providing cutting structure to drill essentially all the way to the center of the hole. Such philosophy was not Without foundation in experience, because such a core, once formed when'drilling with a prior art rock bit, typically grows larger and larger until it erodes through the cone shell of the cutters and exposes the bearing structure in the vicinity of the nose. In this manner the bit becomes unfit for further use long before the remainder of the cutting structure has spent its useful life.

In the cutters and bits of the present invention, each cutter nose has been rounded off in such manner that in operative position the closest approach of the cutter nose to the bit axis is an appreciable distance from the axis of the bit and borehole. A small but significant core is allowed to develop and this core is prevented from growing larger, or at least is kept to a manageable size, by the action of the inserts in the nose of the cone and the manner in which they are disposed in and supported by the cone metal.

This can be more clearly understood by reference to the drawings forming a part of the present specification, in which:

FIGURE 1 is a vertical section of a complete rock bit of the present invention as seen when looking in the direction indicated by the arrows associated with lines 1--1 of FIGURE 2, modified to show in section certain parts that would otherwise appear in elevation and certain other parts contrariwise,

FIGURE 2 is a bottom view of a three cone rock bit of the present invention, each cone thereof embodying the wraparound spearpoint of thepresent invention,

FIGURE 3 is a fragmentary view showing only the compacts of the three cones in a composite view as they are rotated through the plane of the paper, a view familiar to those skilled in the design and construction of rock bits under'the designation compact coverage on bottom.

In FIGURE 2 there are shown three compact cutters or cones 1, 2 and 3 mounted on appropriate bearing pins to form a three-cone rock bit. Since the view is from below the bit, it will be appreciated that the normal clockwise formation-cutting direction of rotation looking downhole from the surface is reversed in FIGURE 2 so that the cones rotate in the counterclockwise direction about the bit axis. Thus cone 1 is followed by cone 2, and cone 2 is followed by cone 3 in making hole. It can be seen that cones 1, 2 and 3 are interfitting in the areas outwardly from'the noses or spearpoints 7, 8 and 9, and inwardly from heel rows of compacts 4, 5 and '6 in that any row of compacts of one cone projects into the groove between adjacent rows of compacts on each of the other cutters. This view also illustrates the gap 10 at the center of the hole defined by the blunt'noses 7, '8 and 9 of the three cutters.

FIGURE 1, a modified partial section as indicated by line 11 of FIG. 2, illustrates a typical rolling cutter rock bit utilizing three of the compact cutters of the present invention. Thus the bit terminates at the top in a hollow pin or shank 11 tapered'and threaded for connection to a drill collar or sub, and includes a generally cylindrical body portion 12 containing a plurality of drilling fluid passageways of which one is shown at 13. Three equally spaced legs 14 extend downwardly from the outer part of body 12, and from each such leg 14 a bearing pin 15 extends downwardly and inwardly toward the vertical axis 16 of the bit. Each such bearing pin may be disposed so that its axis 25, which is also the axis of rotation of the cutter mounted thereon, intersects the other cone axes at a common point on bit axis 16, as in the non- 'oifset design illustrated, or so that its axis isskew to the bit 'axis, as in an ofiset design.

Typically the bearing pin is shouldered and recessed to accommodate roller bearings 17, ball bearings 18 and the shoulder 1% and bushing 29 of the cutter 1, the cutter 1 being similarly contoured on its interior andals'o having an appropriate recess to accommodate thrust button 21. The cutter or cone 1 is mounted on bearing pin 35 with all such elements except balls 18 in place, the latter beingtherea'fter loaded through an appropriate passageway (not shown) in the bearing pin which is afterwards plugged to-secure the balls in their race and lock the cutter against movement axially of the bearing pin. Not shown are passageways frequently provided between the interior of shank 11 through bearing pin 15 to theibear ings, for cooling and lubricating'the latter with drilling fluid, particularly in air drilling.

. In some bits; compacts 23 similar 'to'those in the gage surface 22 of the cutters are inserted in the outside surface of shirttail 27' of the bit leg to resist wear thereof and V to assist in maintaining the hole at full gage.

As the particular compacts and their disposition in and posing that part of FEGURE lrillustrating the cutting structure of cone 1 in contact with theformation on similar partial sections of each of the other two cones. The usual such composite view shows ordy that part of FIGURE 3 lying to the left of and below the center line of the cones, as that appearing to the right and above nose) is used to designate that portion of a'cutteron I which are mounted the compacts shown in the right hand 7 portion of FIGURE 3. Each spearpoint surface 7, 8 or 9 on the group of cutters as awhole form no part of the i present invention, only general comments on such features need be made here. Each compact 39 is typicallycylindrical, is madefofa hard, abrasive material such as cast a or sintered tungstenrcarbidahas a blunt,- ovoid or oglve is a conical surfaceof the cone steel terminating in a fiat or otherwise blunted end, 41 on conel, 42 on cone 2,'and 43 on cone 3 (see FIG. 2). Thespearpoint compacts are disposed so that their cutting extremities define in the formation a similar contour having a considerably greater 7 7 degree of bluntness, i.e., freedom from sharpfedges- This cutting tip. contour may properly, be described as convex,

as in FIGURE 3.

hole bottom adjacent sidewall-24 of the hole, the three heelrows of compactsd, 5 and 6 are disposed to cut coinciding paths in this area[ The gage rows of compacts 31 are prefiattened at their outer ends to obtain more wearresistant surface in this critical area.

1 Each cone has one or. more. intermediate. row of com- Y pacts'betwecn the heel row and the spearpoint, such compacts being inserted in lands on the cutter surface, e.g.

row 34 in land 32 of cone 1.. 'Any intermediate row of compacts does not cut a path overlappinglth'at cut by an.

adjacent row on either of the other cutters, but on the other hand such rowsare disposed fr'omone cutter to the next to cut'adjacent paths Which fullydisintegrate an annulararea of formation. Thus row 33 of cone 3 is fol low'edby row'S-of cone. 1, and thereafter row 35 of cone 2, 'row 36 ofcone 3, and finally row 37 of cone 1. This cooperation of the rows of compacts in covering bot tom is more readilyapparent in FIGURES, Where the "'upper numeral appearing below each compact on the factured and successfully field tested in formations whereicenterline thereof indicates the cone on whichsuch row 7 of compacts is secured and the lower numeral indicates the number'of compacts in that row. i

' It should also .be noted that the above described construction and disposition of compacts in the intermediate l 'rows permit'the preferred interfitting feature illustrated in FIGURES '1 and 2 1With theex'ception of rowj37 of cone 1, and possibly row 3610f cone 3, each of the compacts ineach intermediate row protrudes into argroove in each adiac'ent cone as the cone rotates through their plane'of tangency, i.e., aplane passing through both cone axes. interfitting design has advantages familiar to i" all designers of rolling cutter rock bits, e.g., more space x for the cone 'shell and cutting structure, and the selfcleaning of cutter surfaces:

f Attention is now'in'vited to the predominant feature of the present "invention, the rounding or blunting of each .This is shown particularly in ouses 2 and 3, especially the latter FIGURE 3 may be thought of as a composite sectionof all three cutters madeupjby superim- 7 As is apparent from FIGURE 2, the spearpoint coma pacts on each cone are not only non-interfitting with the spearpoint compacts on each of the other cones, but face such compacts across a considerable space therefrom; In" other words, a plane through the centerlines of any two of the cones (and bearing pins), which shows the nearest approach of one cone to the other, indicates a srnall but detail at the bottom of FIGURE 1,'which includes a.sec-' tion obtained by passing a plane through the center lines of both cone 1 and cone 3. Such a plane, of course, is slanted from the vertical, as a result of which the'nature of the nearest approach of one cone 1to the other is not readily apparent from any exterior .view or vertical section."

It will be apparent from an examination of the drawing 3 .that the spearpoint compacts are not disposed in lands,

and are generally disposed in circumferential rows which overlap one another from a row on one cone to an adjacent row on either of the other two cones. v

' By way of example and contrast, it may be stated that the bit illustrated in the drawing is one extensively manu-v in prior art. bits failed prematurely through erosionofthe spearpoints. Each figure ofthe drawing is an accurately scaled reproduction of the samef9 /s" '(dia.) bit; FIG- IJ RES l and 2 are reduced in size, butFIGURE 3 as sub mitted 'is a' full scale representation of the'compacts' as they are swept through a vertical planepass'ingthrough the bit axis 16. Thus the radius of-the bit and the bore hole cut by the, bit, from bit center line 16 to gage/surface 22 or formation sidewall 24, is 4 4 inches;

, Thecore or post23 not cut bythe 'spearpoint compacts decreases from a maximumdiameter of A" at horizontal line A to a minimum of about A ".at the closest approach of a compact thereto, at horizontal line B of FIGURES. T p A core of such diameter presents no serious impediment I to the progress of the bit in making hole, and'is'apparently broken olf progressively, the broken sections falling'to the hole and being comminuted by thecutters. j 1 As indicated above, the disadvantage of core formations in the "operation of; a rock bit "of the prior art is the premature disintegration of'the spearpoint cutting structure. This early destruction of the spearpoints appears. to result from a chain of events starting with a failure of the cone metalbetweenadjacent compacts Pieces of the metal are fractured and break off, weakening I the structural support for the compacts. Further rotation and vibration aggravate the condition until the compacts themselves fall out, exposing other areas of the cone metal to erosion, such areas frequently underlying the compact holes because of prior spalling. Although the outer thickness of the cone wall will resist erosion for a time by virtue of its case hardening, such abrasion-resistant material wears off quickly relative to the rate of wear of compacts, thus exposing the softer, unhardened inner layer. This layer erodes rapidly to expose the bearing surfaces, at which point cone failure is virtually complete.

In approaching the present invention, it was at first postulated that the desired results would be obtained by blunting the spearpoint and increasing the number of compacts therein relative to the number in a prior art spearpoint of the same size. This thinking was based on the assumption that more compacts would be needed to prevent the core from growing, the thinking being that the compacts in the spearpoint area would now have to cut core as well as bottom. It was soon discovered, however, that the very opposite tack had to be taken, using less compacts in the wraparound spearpoint of the present invention than in the three-spearpoint cutters of the prior art.

Thus the total number of spearpoint compacts in the 9%" bit illustrated in the drawing is 46, of which 14 are on cone 1, 16 are on cone 2, and 16 on cone 3. These compacts are all either or A in diameter and all but the single compact 26 in the very end 41 of cone 1 are either or in length, the exception being /2 long. By contrast, the total number of spearpoint compacts in a standard 9%" dia. three-spearpoint bit of the prior art is 56, of which 17 are on cone 1, 18 on cone 2 and 21 on cone 3. These compacts are also of either /8" or 5 diameter, and all but one are in length, the exception corresponding to the single compact 26 in end 41 of cone 1 as shown and being /8" dia. by long. Thus the sizes of the compacts used are essentially the same, but in the wraparound spearpoint more formation cutting is obtained by using less compacts than are used on the prior art three-spearpoint bit. While the latter has proven adequate in fast drilling in most formations, it has broken down by spearpoint failure in certain types of formations, while the wraparound spearpoint bits of the present invention have drilled the same formations with superior performance.

It is believed that one of the most important factors in the success of the present invention is that the cone metal section between any pair of adjacent compacts has been increased. The importance of this fact may be appreciated by imagining a sectioning plane passing through the axes of a pair of adjacent compacts in any one row. Since the cone periphery is circular in section, the cylindrical compacts mounted normal to the cutter surface will approach one another most closely at the bottoms of the holes in which they are mounted. The metal between adjacent hole bottoms constitutes a potential source of failure, and if the dimension is too small the metal may fracture and break out. The minimum such dimension between any pair of spearpoint compacts in the present invention is about A; inch, a dimension made possible largely by decreasing the number of compacts despite the sacrifice of cone nose metal through rounding. Since the corresponding minimum dimension in the prior artthree spearpoint bit discussed above is about inch, it can be seen that this critical dimension has been at least doubled in the present invention. In this connection it should be noted that the bearing pin 15 and associated bearings 17, 18, 19, and 21 are identical with the prior art bit alluded to above, and that the cone shells are also identical except for the blunting of the nose and the holes for the compacts.

It will be noted that the single 5 dia. by /2" long compact 26 in the end 41 of cone 1 shown in the drawing is slightly cocked with respect to the cone center line 25. While there is nothing particularly critical about such disposition, it may be noted in passing that such disposition permits the particular compact to engage and disintegrate a greater area of formation than would be the case if it were co-axial with center line 25. To appreciate this, it is only necessary to keep in mind that the rolling motion of a conical cutter is a combination of rotation about bit axis 16 and rotation about cone center line 25. The two extreme positions of this compact are indicated as 26A and 26B in FIGURE 3. Cone end 41 is normal to the compact and thus departs slightly from a true normal to cone center line 25 to furnish uniform support for the compact.

While the rolling cutters of the present invention have been described above with reference to a particular size three-Scone rock bit, it is believed to be readily apparent that the invention is not limited to a particular number of cones or size of bit. Thus the number of cones may be four or more, two or even one, the compacts being disposed according to various appropriate schemes now well known in the art. The principles involved may also be applied to other rotary earth penetrating devices using rolling cone cutters, e.g., core drills, reamers and big hole drills. A core drill may be thought of as a rock bit in which the cutters are disposed at a larger radius to leave a relatively large core, and including various well known structures for severing and retrieving a core. The structural features of the present invention-rounding the cone nose, disposing compacts therein normal to the nose surface and reducing the number of compacts therein to provide adequate metal section between adjacent compacts, are readily applicable.

It is also believed to be apparent that the wraparound spearpoint of the present invention may be employed on a rolling cone cutter in which the cutting structure outwardly from the spearpoint consists of steel teeth or combinations of steel teeth and the compact type cutting structure illustrated.

What is claimed is:

1. In a rock bit having a multiplicity of rolling cone cutters mounted thereon with their axes of rotation inclined downwardly and inwardly with respect to the axis of rotation of the bit, wherein each cutter has a conical nose at its small end terminating adjacent but short of said bit axis, such nose having inserts of wear resistant material protruding therefrom with blunt cutting tips and wherein such inserts are disposed and distributed between cutters to roll through adjacent and overlapping annuli, the innermost such annulus being defined by an insert from the apex of one of said conical noses, the

improvement comprising slightly truncated ends on all of said noses and said inserts of wear resistant material protruding from the conical surfaces and some of the truncated ends of said noses with the cutting tips of all inserts adjacent but spaced an appreciable radial distance from the bit axis at their nearest approach thereto, said insert in a nose apex having its cutting tip protruding axially beyond the cutting tips of the other inserts and such other cutting tips being disposed in axially spaced concentric annular rows of progressively increasing radius so that, as all cones are rotated through a common position, such cutting tips of the nose inserts lie within and define a convex surface of revolution surrounding the small end of the cutters, said radial distance being such as to adapt said bit to cut a wellbore leaving a rock post of such a radius that the post disintegrates as drilling progresses, the number and spacing of said inserts in the noses providing supporting cone material between adjacent inserts having a minimum dimension of about inch.

2. The improved rock bit of claim 1 in which said insert in a cone apex is inclined with respect to the cone axis, whereby said insert during rotation and rolling of the cone describes an annular path of greater width than it would if it were mounted concentric to said axis.

s, lea ta 3. In a rock bit in which there are a multiplicity of legs extending downwardly from the head, thereoflbear- 'ing pins extending downwardly and inwardly from said legs toward' the axis of rotation of said bit, and rolling cone cutters rotatably mounted on said bearing pins, such cutters having conical nose portions terminating rotated, such cutting structure including wear-resistant inserts securedin and distributed over the nose portions and protruding, therefrom withblunt cutting extremities, the improvement comprising slightly truncated noses on said cutters and having said wear resistant inserts secured in and protruding from all of the conical peripheries and from some of the truncated ends'of said noses, said inshort of thebit axis and cutting structure adapted to col 'operativ'ely cut rock and define a wellbore as such bit is,

sertsbeing'rotatable with the cone s'through points" in a 7 vertical plane of the bit axis which are adjacent said axis but spaced therefrom an appreciable radial distance, one

of said-inserts being centeredin a truncated end of a nose with its tip extending ax ally of the cone'farther than the tips of the other inserts, said other inserts being disposed in annular rowswith their cutting tips spaced progressively away from the tip of said center insert in the direction parallel to a cone axis, such arrangement being one wherein the insert tips of all cones, when such cones are superimposed on each other in a common position, lie within and define a convex surface of revolution centered on and surrounding a cone nose, said radial distance being such as to adapt said bit to cut a Wellbo're leaving a rock post of such a radius that the post disintegrates as drilling progresses. I

4. The improved rock bit of claim 3 in which the minimum dimension between adjacent nose inserts is at 1east%inch-. V

5. The improved rock'bit of claim 3 in Which said center insert is' inclined with respect to said cone axis,

whereby said insert during rotation and rolling of the cone describes an annular path of greater width than it would if it were mounted concentric to said axis.

References Cited in-the file of this patent V UNITED STATES PATENTS Esseling June 10, I919 1,273,460 France Sept. 4, 1961 nt -ye 

1. IN A ROCK BIT HAVING A MULTIPLICITY OF ROLLING CONE CUTTERS MOUNTED THEREON WITH THEIR AXES OF ROTATION INCLINED DOWNWARDLY AND INWARDLY WITH RESPECT TO THE AXIS OF ROTATION OF THE BIT, WHEREIN EACH CUTTER HAS A CONICAL NOSE AT ITS SMALL END TERMINATING ADJACENT BUT SHORT OF SAID BIT AXIS, SUCH NOSE HAVING INSERTS OF WEAR RESISTANT MATERIAL PROTRUDING THEREFROM WITH BLUNT CUTTING TIPS AND WHEREIN SUCH INSERTS ARE DISPOSED AND DISTRIBUTED BETWEEN CUTTERS TO ROLL THROUGH ADJACENT AND OVERLAPPING ANNULI, THE INNERMOST SUCH ANNULUS BEING DEFINED BY AN INSERT FROM THE APEX OF ONE OF SAID CONICAL NOSES, THE IMPROVEMENT COMPRISING SLIGHTLY TRUNCATED ENDS ON ALL OF SAID NOSES AND SAID INSERTS OF WEAR RESISTANT MATERIAL PROTRUDING FROM THE CONICAL SURFACES AND SOME OF THE TRUNCATED ENDS OF SAID NOSES WITH THE CUTTING TIPS OF ALL INSERTS ADJACENT BUT SPACED AN APPRECIABLE RADIAL DISTANCE FROM THE BIT AXIS AT THEIR NEAREST APPROACH THERETO, SAID INSERT IN A NOSE APEX HAVING ITS CUTTING TIP PROTRUDING AXIALLY BEYOND THE CUTTING TIPS OF THE OTHER INSERTS AND SUCH OTHER CUTTING TIPS BEING DISPOSED IN AXIALLY SPACED CONCENTRIC ANNULAR ROWS OF PROGRESSIVELY INCREASING RADIUS SO THAT, AS ALL CONES ARE ROTATED THROUGH A COMMON POSITION, SUCH CUTTING TIPS OF THE NOSE INSERTS LIE WITHIN AND DEFINE A CONVEX SURFACE OF REVOLUTION SURROUNDING THE SMALL END OF THE CUTTERS, SAID RADIAL DISTANCE BEING SUCH AS TO ADAPT SAID BIT TO CUT A WELLBORE LEAVING A ROCK POST OF SUCH A RADIUS THAT THE POST DISINTEGRATES AS DRILLING PROGRESSES, THE NUMBER AND SPACING OF SAID INSERTS IN THE NOSES PROVIDING SUPPORTING CONE MATERIAL BETWEEN ADJACENT INSERTS HAVING A MINIMUM DIMENSION OF ABOUT 1/8 INCH. 